This study evaluated the effect of single doses of a magnesium/aluminum antacid (MAALOX) given 4 and 6 hours before or after administration of raltegravir, on the pharmacokinetics of raltegravir in human immunodeficiency virus (HIV)-infected participants. The study consisted of Part 1 (Periods 1, 2, and 3) and Part 2 (Periods 4 and 5), with each study period separated by a washout period of at least 2 days; Part 1 was separated from Part 2 by a Pause. Each study period had a duration of ≥2 days, and paused for evaluation of Part 1 pharmacokinetics results before continuing to Part 2. The same participants participated in Parts 1 and 2. The primary hypothesis tested (in Part 1) was that raltegravir plasma concentration 12 hours after administration (C 12 hrs) would not differ significantly from raltegravir C 12 hrs when antacid is administered 4 hours before or 4 hours after raltegravir.